This proposal seeks to acquire a Leica TCS SP8 gated stimulated emission depletion (STED) super-resolution fluorescence microscope for the Center for Cell and Molecular Imaging at Yale University School of Medicine. The ongoing renaissance in the use of light microscopy for cell and molecular biology and physiology has been driven in large part by the development of specific fluorescent probes of cell structure and function, coupled with confocal and multiphoton fluorescence microscope systems that extend our ability to visualize and quantitate such probes in cells and tissues to near the diffraction liit. However, newer 'super-resolution' techniques now provide the potential to observe the subcellular distribution of fluorescent probes well beyond the diffraction limit. The requested gated STED microscope would permit collection of images with spatial resolution approximately five-fold below the diffraction limit. Moreover, in contrast to other super-resolution techniques, for STED imaging a very wide range of fluorescent probes could be used and samples would not require any special preparation beyond what is normally required for more conventional types of fluorescent imaging. Finally, no post-collection processing of images would be required. Specific projects that would take immediate advantage of this equipment include localization of proteins within signaling microdomains associated with lipid rafts in hepatocytes, identification o cytoskeletal and tight junction elements within intestinal epithelia, tracking of synaptic vesiclesin neurons, identification of focal adhesion proteins associated with integrins in endothelia, and examination of vesicles associated with ER biogenesis. By providing access to this unique yet easy-to-use imaging resource, the requested instrument will assure that our investigators will continue to have adequate access to state-of-the-art imaging techniques.